Method and device for manufacturing peel-off lids as well as a peel-off lid

ABSTRACT

A peel-off lid with a rolled-in section around the extraction opening is formed in such a way that before forming the rolled-in section a thin plastic strip is applied onto the collar of the lid ring. After forming the rolled-in section, the plastic strip is melted in order to reach a good adhesion of the plastic on the upper side and the underside of the peel-off lid in the rolled-in section. In this way it is possible to reach a practically hermetic sealing of the cutting edge of the peel-off lid in an inexpensive way and with the possibility to manufacture with high cadence.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of International Patent Application No. PCT/CH2018/000004, filed Jan. 25, 2018, which claims the priority of Swiss patent application 0536/17, filed Apr. 21, 2017, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for manufacturing peel-off lids, a device for manufacturing peel-off lids, and a peel-off lid having a peel-off foil sealing and extraction opening.

BACKGROUND OF THE INVENTION

Peel-off lids are known, e.g. from DE-U 298 17 592 or from DE-U 92 03 953. If the container closed by the peel-off lid contains a liquid, corrosive filling content, e.g. saltwater, the bare cutting edge of the lid opening may corrode. In case of a peel-off lid with a so-called retort-curl a certain protection against the influence of the filling content is reached by rolling in the section with the cutting edge towards the top and outward and by covering it with the peel-off foil. Additionally, the bare or potentially corroded cutting edge, respectively, is not visible. However, traces of the corrosion may nevertheless get visible, depending on aggressiveness of the filling content and storage time of the filled container. EP-A 1 153 840 proposes to seal the peel-off foil also on the roll itself, with the result that the cutting edge is protected from the can content by a sealing. However, it has been noticed that the sealing is difficult to master perfectly at the sealing flange as well as additionally at the roll during production with high cadence. WO-A 02/79041 mentions parenthetically that the gap created during the rolling-in may be filled with the hot-sealing coating of the peel-off foil without describing how this would actually be feasible during the industrial manufacturing of peel-off lids. Known peel-off foils only have a very thin hot-sealing layer and it is not obvious for the skilled person how this layer can be used for gap filling, if a hot sealing known to the skilled person is carried out. The possibility mentioned in WO-A 02/79041 is therefore hardly feasible in practice. It is known from EP-B 2 055 736 how to provide for a container an outward rolling-in at the opening of the container, such that the cutting edge doesn't come into contact with water. It is proposed to apply a protection of the cutting edge with a modified hotmelt material there, which contains a thermoplastic elastomer. WO 2015/164986 A1 discloses a method and a device according to the preamble of the independent claims, which makes possible an effective protection of the cutting edge. In seldom cases an insufficient protection of the cutting edge may arise also for this this known method.

SUMMARY

The invention has the objective of creating an improved method by means of which peel-off lids can be manufactured industrially with very high cadence and with low costs, and for which the number of defective lids having an insufficient cutting edge protection is reduced to virtually zero.

This objective is reached for the method for manufacturing peel-off lids mentioned at the beginning in such a way that after rolling in the free end of the collar, the rolled-in section is heated up in such a way that at least a partial melting of the plastic material of the strip occurs.

The rolled-in section comprises at least the actual retort curl, which follows the section of the lid ring forming the sealing surface and comprises particularly the entire section where the strip of plastic material is present. Heating up is understood in such a way that the rolled-in section is brought to a temperature permitting the plastic material to melt, wherein it is not obligatory but preferred that the entire rolled-in section is brought to the same temperature homogenously. Melting the plastic material is not understood in a way that the entire plastic material of the strip must be brought to the melting temperature. It may be sufficient that the material layer of the plastic material, which borders the lid material, melts in order to ensure the adhesion of the plastic material to the lid ring material. The heating is neither limited to the rolled-in section, it may be that the entire lid ring is heated, however a heating up is preferred that is substantially limited to or concentrated on, respectively, the rolled-in section with the strip of plastic material. For this purpose, a variety of heat sources may be used.

It has been noticed that an optimum adhesion of the plastic material to the two sides of the lid ring can be reached by heating the rolled-in section and melting the plastic material of the strip, which sides border the plastic material of the strip in the rolled-in section. A hermetic tightness of the rolled-in section with respect to the content of the container, on which the peel-off lid is applied, is reached. Thus, corrosion at the cutting edge can be positively avoided at the cutting edge for peel-off lids that were produced according to the invention.

Preferably, the heating up of the rolled-in section is done before sealing the peel-off foil onto the lid ring, such that this is a separate working step during lid manufacturing. In this way it is possible to carry out the heating and the melting of the plastic material separately from the heat introduction during sealing the peel-off foil and an influence of heating up the rolled-in section on the sealing can also be avoided. It is possible to also provide a cooling of the lid ring, e.g. by an air stream, between the heating up of the rolled in section and the sealing, in order not to influence sealing or the sealing parameters, respectively, for the sealing of the peel-off foil on the lid ring.

Preferably, a heating means working inductively is used for heating up the rolled-in section. It generates eddy currents in the metal lid material, which cause it to heat up. The heating may act on the entire lid ring. It may be provided that the eddy currents are generated mainly in the rolled-in section due to the arrangement of the inductive heating means and potentially a concentration of the field lines of the inductive heating by means of pole shoes. A very fast heating up of the plastic material to the temperature triggering the melting of the plastic material may be caused by the inductive heating up of the metal material of the lid ring. Inductive heating means have been used for a long time in the industrial environment for heating up materials and they are known to the skilled person and are also commercially available. Alternatively, the heating up may also be done by means of infrared radiation or hot air.

Furthermore, it is alternatively or additionally possible to carry out the heating up of the rolled-in section while sealing the peel-off foil. In this case preferably a heating means contacting the rolled-in section is provided in the sealing tool, such that a direct heat transfer from the heating means to the rolled-in section takes place. In this way the heating up of the rolled-in section can be carried out separately from the sealing of the peel-off foil on the lid ring, such that the sealing is not influenced in disturbing manner by the heating up of the rolled-in section. It is possible to carry out the heating up in two steps outside the sealing tool, particularly inductively, as well as also additionally inside the sealing tool.

During sealing of the peel-off foil on the lid ring it is known to carry out a double heating up, such that initially a pre-sealing of the peel-off foil on the lid ring occurs, and in a second step the main sealing of the peel-off foil on the lid ring occurs, wherein the temperature of the pre-sealing is smaller than the temperature of the main sealing. In this case it is preferred that the heating up of the plastic material of the strip or of the rolled-in section, respectively, is carried out in the second step during the main sealing of the peel-off foil. In this way it can be avoided that the pre-sealing is influenced in terms of the lower temperature by an additional heat introduction by heating up the rolled in section. Such a heat introduction can be mastered well during the main sealing with the higher sealing temperature.

The term plastic material of the strip comprises in the present context that the strip comprises a polymer or a resin, or consists of it, and that the heating up of the rolled-in section at least to the melting temperature of the plastic material of the strip takes place. Particularly, the heating up of the rolled-in section takes place to a temperature in the range of 100° Celsius to 200° Celsius and particularly to a temperature in the range from 140° Celsius to 180° Celsius. This is particularly advantageous in case the upper side of the lid blank forming the heat-sealable sealing surface for the peel-off foil is a polypropylene-modified varnish system or comprises such, or is a polypropylene-laminated coating or is another polypropylene-containing coating and the underside of the lid blank has a coating made of an inner varnish for cans with polyester or acryl or epoxy or polyvinylchloride. The mentioned material choice of the strip of plastic and the mentioned sections for heating leads to a particularly good connection between the mentioned coatings of the lid blank or of the lid ring, respectively, and the plastic strip.

It is possible to add a foaming agent to the plastic material of the strip, such that foaming occurs during heating up the rolled-in section, which can increase the section or the surface, respectively, of adhesion.

The invention furthermore has the objective to provide a manufacturing device for peel-off lids, by means of which peel-off lids can be manufactured with high cadence and in an inexpensive way, which offer a practically faultless protection of the cutting edge of the peel-off lid against corrosion.

This objective is reached with the device mentioned at the beginning having a series of processing stations.

By means of the at least one further processing station, which is provided after the third processing station in transport direction, which is adapted to heat up at least the rolled-in section of the peel-off lid to at least the melting temperature of the plastic strip, an optimum adhesion of the plastic material on the two sides of the lid ring can be attained with the device by heating up the rolled-in section and melting the plastic material of the strip, which two sides both are adjacent to the plastic material of the strip in the rolled-in section. For the lids manufactured by the device, a hermetic tightness of the rolled-in section is reached with respect to the content of the container on which the peel-off lid is applied. In this way the corrosion of the cutting edge can be positively avoided for peel-off lids manufactured by the device according to the invention.

The rolled-in section is normally a retort curl following the sections of the lid ring forming the sealing surface. Heating up, which is reached by the processing station, is understood in such a way that the rolled-in section is brought to a temperature allowing a melting of the plastic material, wherein it is not necessary but preferred that the entire rolled-in section is brought to the same temperature in a homogenous way. Melting of the plastic material is not understood in such a way that the entire plastic material of the strip has to be brought to the melting temperature. It may be sufficient that the material layer of the plastic material, which is adjacent to the lid material melts in order to ensure adhesion of the plastic material to the lid ring material. The heating up is neither limited to the rolled-in section, it may be that the entire lid ring is heated up, however a heating up is preferred, which substantially is concentrated on the rolled-in section. Arbitrary heat sources can be used for this purpose.

In the subsequent processing station an induction heating means is preferably provided as heat source. This allows a particularly fast heating up of the lid ring, and particularly of its rolled-in section, to the desired temperature which is necessary for melting the strip of plastic. Thus, the high manufacturing cadence for peel-off lids can be maintained also with the additional processing station. The further processing station may be provided at an arbitrary position along the transport path of the device between the processing stations manufacturing the rolled-in section and the sealing station. It may be arranged before or after a flipping station of the device. The arrangement before the flipping station is advantageous because in this way the lid rings were cooled down again until the sealing station. For cooling them down, an additional cooling station may potentially serve, which cools the lid rings e.g. with an air stream. The cooling before the sealing station has the advantage that the sealing parameters are not influenced by the previous heating up of the lid ring.

It may however also be provided that the further processing station is integrated into the at least one sealing station and has a heating means contacting the rolled-in section in the sealing tool. For a device having two sealing stations in succession in transport direction, in order to carry out a pre-sealing of the peel-off foil and the main sealing, the further processing station is preferably integrated in the second sealing station.

The further sealing station is particularly adapted to heat up the rolled-in section in the temperature range from 100° Celsius to 200° Celsius and particularly in the range from 140° Celsius to 180° Celsius. Furthermore it is preferred that the application station is adapted for applying the band-shaped plastic strip in such a way that a strip with a substantially uniform thickness, particularly a thickness in the range from 0.05 mm to 0.5 mm and particularly with a thickness of around 0.1 mm is generated for applying the band-shaped plastic strip. The low thickness of the strip is advantageous for reaching the melting temperature fast.

Furthermore, the invention relates to a peel-off lid comprising a circumferential attachment section, a sealing flange with a peel-off foil sealed onto it, and a rolled-in section extending in a circumferential way around the sealing flange, which limits the extraction opening laterally, wherein the rolled-in edge has a sealing made of a plastic, which term means a polymer or a resin, which is connected to the upper side and the underside of the peel-off lid in an adhesive way by melting the plastic in the rolled-in section. This lid has the mentioned advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments, advantages and applications of the invention result from the dependent claims and from the now following description by aid of the figures. Thereby it is shown in:

FIGS. 1 to 5 show vertical section views through a lid blank, a lid ring and a peel-off lid for describing processing steps when manufacturing a peel-off lid;

FIG. 6 shows a vertical section view of a lid ring during manufacturing of a peel-off lid according to the invention;

FIG. 7 shows a magnification view of a part of the lid ring of FIG. 6;

FIG. 8 shows the lid ring of FIG. 7 after rolling in the edge of the extraction opening for forming the rolled-in section of the lid ring;

FIG. 9 shows a magnification view of a part of the lid ring of FIG. 8;

FIG. 10 shows a top view on the lid ring of a peel-off lid;

FIG. 11 shows a schematic side view of a device according to the invention for manufacturing peel-off lids with sealed cutting edge according to the method of the invention;

FIG. 12 shows a vertical section view of a part of a sealing tool for carrying out the heating up of the rolled-in section in the sealing tool; and

FIG. 13 shows an illustrative view of the vertically cut sealing tool of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 11, the manufacturing of peel-off lids according to the prior art, known to the skilled person, can be shortly explained. FIG. 1 shows a lid blank 1. A stack 12 is shown at the beginning of the transport path of a manufacturing device 20 (FIG. 11), which contains a plurality of such lid blanks which are individually destacked and processed by different processing stations along the transport path, wherein firstly lid rings are formed from the lid blanks and are subsequently further processed until the finished peel-off lid. The lid blanks are e.g. round disks made of coated metal, which are thereby protected against corrosion, e.g. made of coated tin plate. The coating of the underside located at the top in FIG. 1 is normally different from the coating of the upper side of the blanks 1, which are located at the bottom in FIG. 1. These blanks have e.g. a diameter of 11 cm and have been preformed at their edge 6 by a not shown processing machine and the shape of the edge 6 serves later to attach the finished peel-off lid on a container or a can, respectively, by a fold joint. This is known to the skilled person and is therefore not described here in more detail. The lid blank 1 of FIG. 1 and the lid rings 2 of FIGS. 2 to 4 are shown with their underside facing upward, as mentioned, while the finished peel-off lid of FIG. 5 is shown with its upper side, and therefore with the peel-off foil 8, showing upward. The processing in the device can initially be done in the position of FIGS. 1 to 4, whereafter a turning station 26 follows, which brings the lid rings into the position of FIG. 5 for sealing the peel-off foil 8 onto the respective lid ring.

The transport device 22, which transports the lid blanks, the lid rings and the peel-off lids in the manufacturing device 20 along the transport path in direction of arrow A from a processing station to the next processing station, is particularly formed by two parallel toothed belts having receptacles for the lid blanks or the lid rings, respectively, as known by the skilled person from WO 2006/017953. This is also not described in more detail here. In the processing stations, which are known to the skilled person and are only shown schematically here, each of the blanks to be processed is lifted by the transport device 22 and processed by the respective processing station and returned to the transport device 22. This is indicated at the processing stations with the arrows showing upward and downward. The drive of the processing stations is indicated for each processing station below the transport device. It serves to lift and lower the blanks and the lid rings and to carry out the respective processing steps.

In a punching processing station 23, first a lid ring 2 is formed from the lid blank 1 by cutting out a middle section 30 of the blank and discharging it as waste. In this way the extraction opening of the peel-off lid is formed, which is sealed with the peel-off foil in a later manufacturing step. A sealing flange 7 is left, following the extraction opening 15. The metal material is exposed at the cutting edge 31 or the metal sheet of the lid ring 2 is not protected there anymore by the coating or the coatings, respectively. The edge of the extraction opening is drawn upward as a collar 4 in a processing station 24 and this collar is rolled in a further processing station, such that a so-called retort curl 5 is formed. The shape of the rolling-in or of the retort curl, respectively, may be different. The rolling-in forming the edge of the extraction opening makes sure that the user of the can is protected from the sharp-edged cutting edge 31 during extraction of the can content.

If the processing steps are carried out with the sealing flange 7 oriented downward, as shown, the turning station 26 follows, which turns around the lid rings such that during further processing the sealing flange 7 lies after the turning station on top in the transport device 22 and in the processing station.

Thereafter, the peel-off foil 8 is sealed onto the sealing flange in two steps, with a first sealing station or pre-sealing station 27, respectively, and a second sealing station or a main sealing station 28, respectively. The sealing process is also known to the skilled person and is not described in more detail here. Further processing stations may follow, in which a stamping of the sealing foil is carried out, the peel-off latch is positioned and a tightness examination is done. This is also known to the skilled person and is not described in more detail here. At the end of the manufacturing device 20, finished peel-off lids 10 (FIG. 5) are produced, wherein a peel-off foil 8 is spanned over their extraction opening 15, which peel-off foil is sealed on the sealing flange 7. The edge of the extraction opening 15 is formed by a retort curl 5 bent upward and outward (in the position of the lid according to FIG. 5). The finished peel-off lid 10 can be attached to a can shell (which is indicated in FIG. 5 only by a wall part 11) by means of its folding edge 6 and thereby seals the can. This is done during the filling operation, during which the can has been filled with a filling content. The filled can may be opened later by tearing off the peel-off foil from the lid ring by means of its peel-off latch 18, such that the extraction opening 15 is open.

In the following, the process for applying a strip made of plastic material in the rolled-in section, known from WO 2015/164986 A1, and the process according to the present invention are described, wherein it is also referred to the known manufacturing steps described above or the known manufacturing device, respectively, if necessary.

FIGS. 6 and 7 show a lid ring for which the processing step of drawing the edge of the extraction opening for forming the collar 4 has already been carried out. This was done in the processing station 24. For the shown preferred example (or in a separate step) a curvature to the inside was created at the upper end 34 of the collar 4, which simplifies the later rolling-in for forming the retort curl. Furthermore, a plastic strip 32 was attached to the inner side 40 of the collar 4 in a work step. The application of this plastic layer is done in a separate processing station 29 arranged between the drawing station 24 and the rolling-in station 25.

The band-shaped strip 32 made of the plastic material forms during rolling in a sealing for the cutting edge 31, which is shown in the following. The strip 32 consists of a plastic, wherein this term is also intended to encompass a polymer or resin. Such plastics are commercially available and particularly also available of qualities making them able to reliably withstand the sterilisation temperature during sterilisation of the filled container and consequently don't melt again at sterilisation temperature, such that the sealing formed by the strip is maintained during the sterilisation. The strip is preferably formed with a uniform thickness along the entire height of the band, as shown. It is provided as thin plastic strip, preferably having a thickness d in the range between 0.05 millimeters and 0.2 millimeters, preferably a thickness of about 0.1 millimeters. The height H of the strip may e.g. be between 1 and 3 mm.

The application is preferably done in the way known by the skilled person from WO 2015/164986 A1 by injecting melted, liquid plastic material, wherein a relative movement of nozzle and lid ring occurs. Preferably, the lid ring is moved rotationally in the processing station 29 and during this the inner side 40 of the collar 4 is moved past the outlet opening of an injection nozzle arranged statically during application, out of which the plastic emerges. The lid ring is therefore lifted in the processing station 29, rotated, and the application is activated when the lid ring has reached the correct position with respect to the outlet opening. After at least a full rotation, if a band running without gaps past the inner side or such a strip is formed, respectively, the lid ring is again moved downward towards the transport device, wherein the rotation is terminated, such that the lid ring can be placed on the receptacles of the transport device. Thereafter, the transport to the rolling-in station 25 occurs. The plastic of the band 32 already cools down during application on the lid ring and solidifies, such that no flow of the plastic occurs during the subsequent transport and the band is stable in the shown shape. If necessary, a cooling means, e.g. as a fan, may be provided in the application station or the processing station 29, respectively.

During application it is made sure that the distance of the outlet opening or the injection nozzle, respectively, to the inner side 40 of the collar 4 remains substantially constant during spraying of the liquid plastic, such that the thickness of the strip 32 remains substantially constant and its small thickness is made possible. This can be done in the way known from WO 2015/164986 A1. The procedure according to WO 2015/164986 A1 for generating the strip 32 is preferred. Within the scope of the present invention the strip 32 may however be also applied onto the lid ring in other ways. Hence, it is possible to lay a prefabricated strip made of plastic material into the collar of the lid ring. This may be done in a separate processing station or during drawing the collar in the station 24 or during rolling in the collar in station 25. In these cases the shown station 29 would be obsolete.

It can be seen that the strip 32 is positioned at the inner side 40 of the collar 4 in such a way that it is located closer to the plane of the sealing flange 7 than to the cutting edge 31. The positioning and dimensioning of the strip is approximately such that the strip 32 covers the lower third of the collar 4 up to approximately the lower half of the collar 4. A greater height H of the strip is possible, however the material quantity for the used plastic increases without being necessary for the further processing or for the protection of the cutting edge, respectively. The height H is of about 1 mm to 3 mm in practice.

The lid ring provided with the plastic strip according to FIGS. 6 and 7 is provided with a retort curl 5 in a known way in the processing station 25. This station 25 works with the rolling-in tools known for this purpose, such that this doesn't have to be described here in detail because it is known to the skilled person. A modification which is obvious for the skilled person results potentially for the tools, if the collar 4 has already been bent at its upper edge 34 for the rolling-in, which is preferred. It can be seen according to FIGS. 8 and 9, which show the lid ring after the turning station 26, that the strip 32 forms a seal during the formation of the retort curl 5, which avoids entry of liquids into the interior of the retort curl. In this way, the bare cutting edge 31 is protected against the influence of a liquid located inside the can. For this purpose it is irrelevant if the rolling-in is done such that the cutting edge 31 is partially embedded in the strip 32, as illustrated, or if it only lies at the strip 32. Even the contrary, that the cutting edge 31 cuts the strip 32 and lies at the metal of the inner side 40, doesn't hinder the function of the strip 32. Thus, normal manufacturing tolerances during formation of the retort curl 5 don't play a role. The top view of FIG. 10 shows the lid ring as it is transported in the sealing station 27, where the peel-off foil is sealed onto the extraction opening 15.

In the example of FIG. 11 the manufacturing device 20 for the peel-off lids comprises the processing station 29 for applying the band 32 on the lid ring and the processing station 25 for rolling in the collar 4.

According to the present invention, the rolled-in edge section is heated up in order to melt the strip 32 at least in the contact area to the metal of the lid or to the coatings located thereon. The rolled-in edge section comprises at least the retort curl 5, as it is for example indicated in FIG. 9, and particularly the entire part of the peel-off lid, which is covered by the strip 32. For a first exemplary embodiment, a processing station 35 is provided before the turning station 26, in which processing station 35 the heating up of the rolled-in section is carried out. This may be done in such a way that for this processing station 35 the lid is also lifted up from the transport means 22 and is subsequently heated up in the processing station and then placed on the transport means. The lid ring or its rolled-in section, respectively, may however be equally heated up in the processing station while it is located on the transport means 22, thus without lifting it up from the transport means. In the processing station 35 before the turning station the lid ring still lies with the retort curl or the rolled-in section, respectively, showing upward, as shown in FIG. 4. This makes possible that the rolled-in section is heated up from above and preferably an induction heating device is provided for this in the processing station 35, which is shown schematically as a block 43. The embodiment of such a heating device is known to the skilled person and doesn't have to be described here in more detail. Instead of an induction heating device it would also be possible to provide an infrared radiation source or a hot air source.

In another exemplary embodiment, the processing station may be provided for heating up the rolled-in section after the turning station and it is shown with interrupted lines as processing station 35′ in the illustrated example. In this processing station the rolled-in section lies at the bottom and it is accordingly preferred that the heating source acts from below, such that it could be more advantageous to design the processing station 35′ in such a way that the lid ring is lifted from the transport means 22 therein in order to carry out the processing with the heating source. Also in this case an induction heating or another type of heating may be provided, which is only shown schematically as block 43.

After the heating up of the rolled-in section it is possible to provide a cooling, e.g. by a fan. This is particularly advantageous if the processing station 35′ is present after the turning station 26 and furthermore a pre-sealing station 27 for pre-sealing the peel-off foil 8 is provided on the sealing flange 7. Apart from that it is possible that an undesired influence of the temperature for the pre-sealing occurs by heating up the rolled-in section.

Alternatively to the heating up in a processing station 35 and 35′ or additionally to it, the heating up of the rolled-in section may be carried out in the sealing tool of the sealing processing station. In case of the pre-sealing with the processing station 27 and the main sealing of the peel-off foil with the processing station 28, it is preferred that the heating up of the rolled-in section is done in the main sealing station 28. FIGS. 12 and 13 show exemplarily the structure of a sealing tool for sealing the peel-off foil and for heating up the rolled-in section. FIG. 12 shows a detailed view of the bottom part 36 of the sealing tool, on which a lid ring 2 lies, which was lifted up from the transport means 22 by the sealing tool. FIG. 13 shows the bottom sealing tool in an illustrative view and already after the sealing step with the peel-off foil 8 on the lid ring 2. In the known sealing step, which is not described here in more detail, a fitting sealing foil is placed on the lid ring and is attached to it on the sealing flange 7 by the sealing process by means of the upper—not shown—sealing tool, whereafter the peel-off lid is placed on the transport means 22. In the figure it is visible that the sealing tool has a special heating means 38 which contacts directly the rolled-in section and particularly the retort curl 5 in order to introduce the heat of the heating means 38 into the rolled-in section for heating it up and for melting the strip 32. The heating energy for the heating means 38 is provided in this example by the heating elements 39, which also serve for heating the lower sealing tool below the sealing flange 7. These heating elements 39, which are heated up electrically, are in direct connection with the sealing tool and are in heat flow contact with the heating means 38 via a heat transfer layer 42. This is a preferred example, however it is obvious for the skilled person that the heat generation for the heating means 38 for the rolled-in section can also be provided in other ways. After leaving the sealing station 28, not only the peel-off foil 8 is sealed onto the peel-off lid but also the adhesion of the strip 32 to the two surfaces of the peel-off lid has been improved by melting the strip 32.

According to the invention, a peel-off lid 10 with a rolled-in section of the extraction opening 15 is formed in such a way that before forming the rolled-in section a plastic strip 32 is applied onto the collar of the lid ring. After forming the rolled-in section, the plastic strip is melted in order to yield a good adhesion of the plastic on the upper side and the underside of the peel-off lid in the rolled-in section. In this way, a practical hermetic sealing of the cutting edge 31 of the peel-off lid is reached in an inexpensive way and with the possibility for manufacturing with high cadence.

While preferred embodiments of the invention are described in the present application, it is clearly noted that the invention is not limited thereto and may be executed in other ways within the scope of the following claims. 

What is claimed is:
 1. A method for manufacturing peel-off lids, for which a lid ring with a central extraction opening surrounded by a seal flange, is formed from a lid blank by a punching process; the edge of the extraction opening is formed by drawing towards a collar protruding away from the seal flange; a strip made of plastic is applied onto the inner side of the collar; the collar is rolled in at its free end and comes to lie in the strip made of plastic; and a peel-off foil is sealed onto the sealing flange; wherein after rolling in the free end of the collar, the rolled-in section is heated up in such a way that at least a partial melting of the plastic material of the strip occurs.
 2. The method according to claim 1, wherein the heating up is carried out before the sealing of the peel-off foil onto the sealing flange.
 3. The method according to claim 1, wherein a heating means working inductively is provided for heating up.
 4. The method according to claim 1, wherein the heating up of the rolled in section is done during the sealing of the peel-off foil on the sealing flange by a heating means contacting the rolled-in section in the sealing tool.
 5. The method according to claim 4, wherein the sealing of the peel-off foil is a two-stage process, comprising firstly a pre-sealing and in a second step the main sealing of the peel-off foil onto the lid ring, and wherein the heating up of the plastic material of the strip is done during the main sealing of the peel-off foil.
 6. The method according to claim 1, wherein the plastic material of the strip comprises a polymer or a resin or consists of it, and the heating up is done at least to the flow temperature of the plastic material of the strip, particularly wherein the heating up is done in the range from 100° Celsius to 200° Celsius and in particular in the range from 140° Celsius to 180° Celsius.
 7. The method according to claim 1, wherein the upper side of the lid blank forming the sealing surface for the peel-off foil has a heat-sealing-suitable coating consisting of or containing polypropylene, and in that the underside of the lid blank has a coating consisting of interior varnish for cans or containing interior varnish for cans.
 8. The method according to claim 1, wherein a foaming agent is added to the plastic material of the strip.
 9. A device for manufacturing peel-off lids, comprising a transport installation for lid blanks, lid rings and peel-off lids, as well as processing stations, which are provided in transport direction (A) in succession for processing the lid blanks, lid rings and peel-off lids, wherein a first processing station is provided as punching station for forming a lid ring from a lid blank, a second processing station is provided for forming a collar of the lid ring, which protrudes away from the underside, and a third processing station, wherein the third processing station is adapted to form a rolled-in section from the collar, and wherein additionally at least a sealing station is provided, which is adapted for sealing a peel-off foil onto a sealing surface of the respective lid ring, wherein an application station is provided in transport direction between the second processing station and the third processing station, which is adapted to apply a circumferential, endless plastic strip onto the inner side of the collar, and the third processing station is adapted such that the rolled-in section comes into contact with the plastic strip, wherein at least a further processing station is provided in transport direction (A) after the third processing station, which is adapted for heating up at least the rolled-in section to at least the melting temperature of the plastic strip.
 10. The device according to claim 9, wherein the further processing station has induction heating means.
 11. The device according to claim 9, wherein the further processing station is integrated in the at least one sealing station and has a heating means contacting the rolled-in section in the sealing tool.
 12. The device according to claim 11, wherein two sealing stations are provided one after the other in transport direction, and wherein the further processing station is integrated in the second sealing station.
 13. The device according to claim 9, wherein the further processing station is adapted to heat up the rolled-in section in the temperature range from 100° Celsius to 200° Celsius and particularly in the range from 140° Celsius to 180° Celsius.
 14. The device according to claim 9, wherein the application station is adapted to apply a band-shaped plastic layer having a substantially uniform thickness, particularly a thickness in the range from 0.05 mm to 0.2 mm and particularly with a thickness of about 0.1 mm.
 15. A peel-off lid comprising a circumferential attachment section, a sealing flange, with a peel-off foil sealed onto the latter and a rolled-in section extending circumferentially around sealing flange, which limits the extraction opening laterally, wherein the rolled-in edge has a sealing made of a plastic, particularly of a polymer or resin, which is connected in an adhering way to the upper side and the underside of the peel-off lid by melting the plastic in the rolled-in section. 